Process for the desulfation of coagulation baths for the spinning of viscose



June 2o, 195o 2,512,266

' L. CAUTE PROCESS FoR TRE DESULFATION .oF COAGULATING BATHS FoR THF SPINNING oF vIscosE Filed July 17, 1947 ATYO/PIVEY Patented June 20, 1950 enociiss ernannt `DEsUL-'FATI0N` on o o;- Aeum'rrcmv BAT-Hs Fon THE SPINNING.r

oF ylsooss inoue-v cau-ee; Paris,

Lille, France? Applicationuelyfir;1947, seriam; 761,566* InFr'anceAugustlS; 19'42 y Section 1;. Bublicl Law 690,3 Augs't8g119`4i` Patent expires Aug-ust 13,1196@l This invention relates: to a process.n for the` desulphationA of coagulationbathsffor` the spinningofI viscose.-

It is known.- that m mills producing; artificialtextiles (rayon-,: .branneo employingfthe lviscoseV process, `the coagulationismbtained byl the ,-pas" acid, which*E enriches: this-i bath insodium-fsulphate, a product.L the excessvofi which mus-t be4 eliminated.

This elimination is carried into effect=by causf ingthe sodiumsulphate to crystallize by: the

cooling of a1 part?` of-= thefbalthtincirculation in:`

the. manufacturing@ process-..

According. to f the contentvinil sodium. sulpl'late'A which can be tolerated in the bath, content which variesl according; toi the: product whichI itis. desiredrto obtain; it' is--necessaryvY to treat; inthe. separation installation, a` bath `more-or l less.- rich in :sodium sulphate.' Besides lthis salt it williJ beappreciatedl that-.the other productsY of ',therbath.- also" coexist, su'chfas-aA sul-phurie.-acid; zinovsul-r phatef. sulphate of magnesia; .and so? forth-,- or-L ganic materials and so onse Itresultsfthat accordingfto thecomposition` of the bath to be coole'dg-Vthe+crystal1ization ofthe 'sodium' sulphate will start ata moreV orf less high temperatureY andz that; in-l order to 'obtainsuicient separation; it. will ba required towcool i the @bath treated at? afmorefor less'rlow-P temperaL Y ture; it has been found that in practice it; is. alwayssnecessaryito cool to at least 10 C., often even in the vicinity of C., and sometimes below 0 C. The obtainingof` such temperatures requiresa--sourceofl cold'fof sufficiently low temperature in which it is sufficient tol'obtain a temperature. ofr C., `Ait israre thatit is possible continuallyto haveV available' thewater at a temperature of from 0 to 5? of'the bath2t0-10 C.H l

' Mbreoverrit should-rbedated-1f that infr certain' cases since in general, in factories a certain quantity of water has to be evaporated, that the bath treated to eliminate the sodium sulphate could be a bath previously concentrated.

Up to now the crystallization installations worked in conformity with two processes recapitulated hereinafter: First process:v cooling of the 'bath by means of a cold-producing brine.

'Ihen the factory has available a refrigerating machine cooling a cold-producing brine to the desired temperature and the brine circulates in the crystallization apparatus of known type.

It will be understood that with a view to reducing the consumption of units of cold, it is C., for the cool-ing" ziclaisis.' (c1. 1'8"-54).

possible tok cause' .Y the cooled.:

In'` spite. off ally.y this process.'has the disad-l vantage of requiring'. aconsiderablef amount fof' units` of cold the costfofywhichis high. Morey over the f temperature differencesfemployedarel relatively slight softhat'the surfaces of. exchange-- mustibenconsiderable and since it:n is necessaryfor them` to4 be of metall incapable:- ot beingf attacked' byf sulph'uricacid, the; initial cost of l the samer-and theicostifofi upkeep; is highy f Secondiprocess: coolingfof the -bathriby expansion and Ifl the bath Ato' =be `cool-eddeefbroligflit into ia: space- Whiclr is@ under.` veryf: high vac'i'ium,v correspond ing'rto. an absolute: pressuretof. -a'iI few millimeters ofrmercuryg. the#l bath .e'vaporates':` owing.' to r itsl sensitive: heat' and the: heat. liberated byA the: crystalliza-tienu'- of f Nazt. izf ltewcve-i', it:

willLA bevunderstood that" in:` order? to".P ensure wfor example that'theflboilingiftemperaturevof the bath may be 10 C., considering thatitheflooiling'point'` of ther bathfis approxim'ateiyf? C., 7greater than thatcofwater;` thefabsolutefpressure of the coole The" productioni.- of. vsuchza highl vacuum'` can onfiyfbef'carried into` effets-,l by the welllknownfcombination'i of af-z steam@ ejector: coirlibi-ned'ry Witlf af v'acuunti pum'pi a'ccording to` an.`V arrangement? analogous` to that diagran'iinatically illustrated vacuumv pump l thi ou' h Coldwater inletf arfdl'' l tffavvvaterfreturm This apparatus has the great disadvantage of consuming enormous quantities of steam at the ejector considering the great volume occupied by the bath evaporation pump under such a low pressure.

With a view to reducing this steam consumption and Without changing the principle hereinbefore referred to, the total expansion of the bath has been dividedinto several stages under increasing vacuum by providing at each stage a steam ejector appertaining thereto. In spite of all, the consumption of driving steam remains on the whole very high.

The present invention relates to a process in brine .'refrigerator'.l tobe f preceded by`V anotherl cooler wherein the coldv is produced by the Water or bythe bath already- 3 which the cooling and the subsequent crystallization of the bath are obtained by placing yas previously, the bath in a space wherein there is found a very high vacuum. But in this process the btaining of the vacuum is entirely different.

The principle is known, of the sulphuric acid refrigerating machine wherein the cold is obtained by evaporation of any desired solution under a very high vacuum (the vapour emitted being absorbed by the sulphurifc acid which is diluted owing to this, and which is concentrated later to be reintroduced into the circuit).

This process has not been often applied owing to the cost and the difliculties of reconcentration of the diluted sulphuric acid. The applicants have had the idea of applying this principle to the treatment of spinning baths with most' advantageous results. For it is found that in artiiicial textile mills large quantities of sulfuric acid 'are employed, and this acid may be used, before being employed in the manufacture, for the absorption of the vapours emitted in the bath crystallization apparatus.

Fig. 2 shows a plan of apparatus which may be used for the application of the present invention. The bath to be cooled reaches at I I a crystallization apparatus I2 by'expansion under high vacuum of type known in itself and I3 designates the extraction of the bath and of the salt; this crystallizer I2 is connected through the conduit I4 to a sulphuric acid washer I5 wherein circulates the -sulphuric acid fed at I6 and emerging at I'I. In this washer, the vapour produced by the evaporation of the bath owing to the heat yielded up by its own heat and by the heat'from the crystallization of the sodium sulphate, is absorbed by the sulphuric acid. It results that the ejector I-8 which produces the vacuum only has to carry along the gases incapable of condensation and not, as in the preceding process, all the evaporation vapour. Consequently, the consumption of steam of this ejector arriving at I9 will be inflnitely small as compared with the consumption in the former process.

But this process presents another surprising interest. By way of example, it has been found that to obtain a temperature of 10 G., for the cooled bath, it would be sufcient to have an absolute pressure of 5 to 6 mm. of mercury; it will be necessary, it will be appreciated, that the pressure of the sulphuric acid circulating in I5 remains constantly lower than this value, that is for instance 4 mm. of mercury; according to the concentration of this acid, the latter may therefore have a temperature which would be for an acid of 70% H2SO4, 42; 72% H2504, 47; '74% H2SO4, 51; '76% H2SO4, 55; 78% H2804, 65; 80% H2804, 70; 82% HzSOfi, 81.

The calories liberated by the bath at a temperature of 10 will then be found in the sulphuric acid circulating in the absorber I5 at a much 4 higher temperature and being able to be for example from to 80 C. with acid at 80-82% H2504. n i

Therefore at the same time revalorization has been aiected yof the liberated calories which were unusable when they were 'available at a temperature of 10 C., but which may be used very readily at a temperature of 'Z0-80. They may be used for any desired purpose, for example by absorbing them by a bath circulation, or by a water circulation, in such manner 1as to obtain hot water for which there is always a call in such factories. In the figure, 2| designates a circulation pump for the sulphuric acid, 22 is an extraction Iof the diluted acid, 23 a feed of fresh acid and 2d a circulation of liquid to be heated in the exchanger 20.

Thus by this process not only the steam consumption is reduced to a great extent, but also revalorization is effected of the calories liberated by the low-temperature bath.

The preceding -description has been given by way of example: it is understood that this invention remains valid if the absolute pressure be different from that taken as example.

The expansion apparatus could likewise be divided into several stages working under increased vacuum without thereby altering the principle. The bath could likewise be partially cooled prior to its final cooling in the installation hereinbefore described.

The ejector, that is to say, the device extracting the gases incapable of condensation, could be replaced by an apparatus especially for this purpose; -a vacuum pump of any suitable type.

1. A process for the elimination of sodium sulphate from viscose coagulation baths, comprising passing the bath containing the sodium sulphate through at least one reduced pressure zone for effecting evaporation and cooling thereof, effecting an absorption of the heat of the vapors due to evaporation by sulphuric acid, maintaining -a reduced pressure in respect to the sulphuric acid, and regaining the heat absorbed by the sulphuric acid for utilization thereof.

2. A process according to claim l, wherein the sulphuric acid has a relatively high temperature depending on its concentration for the purpose of facilitating the recovery of the absorbed vapor heat.

LOUIS CAUTE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,873,329 Ritchie et al. Aug. 23, 1932 2,409,624 Granville Oct. 22, 1946 

1. A PROCESS FOR THE ELIMINATION OF SODIUM SULPHATE FROM VISCOSE COAGULATION BATHS, COMPRISING PASSING THE BATH CONTAINING THE SODIUM SULPHATE THROUGH AT LEAST ONE REDUCED PRESSURE ZONE FOR EFFECTING EVAPORATION AND COOLING THEREOF, EFFECTING AN ABSORPTION OF THE HEAT OF THE VAPORS DUE TO EVAPORATION BY SULPHURIC ACID, MAINTAINING A REDUCED PRESSURE IN RESPECT TO THE SULPHURIC ACID, AND REGAINING THE HEAT ABSORBED BY THE SULPHURIC ACID FOR UTILIZATION THEREOF. 